This invention relates to a three phase ripple control system, so called because a control signal, normally of audio frequency is injected onto the normal distribution conductors, usually those supplying power to the equipment to be controlled, in the form of a `ripple` or modulation of the basic current flow.
Ripple control is already well known, but the majority of ripple control schemes in operation at present use shunt injection systems. The injection signal source is connected between line and neutral and thus has to supply power to both the load and the mains power source, resulting in a large injected signal power wastage in the mains source. A series injection system with the generator in each line avoids this power wastage, but in this case the injection signal source is connected in series with the mains supply and therefore has to carry the entire load current without adverse effect.
Another method of achieving series injection employs a transformer of single phase construction, with its secondary connected in series in the mains supply line. This therefore only presents its leakage impedance to balanced three phase load currents. The impedance presented to zero sequence depends on the impedance of the injection signal generator at supply frequency and will usually be large compared to the mains source impedance; this leads to a mains frequency voltage drop across the transformer due to zero sequence current and to undesirable mains frequency voltages and currents being induced into the injection signal generator.